Vacuum tube amplifiers for guitar are unsurpassed for their musicality. Historically, vacuum tube amplification was the only technology available at the dawn of the electric guitar and, as such, established tonalities that have become iconic and remain unsurpassed. Moreover, these musical sounds are still greatly sought after these many decades later. Newer technologies have sought to rival or replace vacuum tubes, usually in pursuit of economy, but have not yet succeeded. Transistorized amplifiers, for example, remain intrinsically limited because their technology, when overdriven, produces dissonant, abrasive sounding harmonics, which is not at all the desired musical distortion of overdriven vacuum tubes.
More recently, modeling technology has made inroads in the amplification market as it uses computer algorithms to basically “replay” sampled (i.e., pre-recorded) tonalities that are then triggered by the guitar. The pallet of available modeled tones invariably emphasizes a selection of well-known vacuum tube amplifiers, including many that are overdriven, again attesting to their lasting desirability. However, despite the convenience modeling offers, it lacks the expressively dynamic feeling produced by an authentic vacuum tube amplifier and leaves most players less than satisfied, and even less inspired due to its sterility. At best, the sound is a “good facsimile” but short of “the real thing.” That elastic “tactile feedback” sensation the guitarist feels in his hands due to the dynamic characteristics of a high-voltage vacuum tube amplifier, especially one driven into and beyond the threshold of saturation, is a major factor in inspiring the musician's playing.
The most hallowed of overdriven tube distortion originates in the power output section of the amplifier. Many of the earliest blues players simply turned up too loud and found that the distortion harmonics generated by clipping the output tubes added greatly to the tonality and expressiveness of their guitar. These are the overdriven electric guitar sounds that became iconic foundations of tone. Blues music led to rock and roll and on to the stylistic extremes found today such as “heavy metal” which rely entirely on massive amounts of added harmonic distortion.
However, power amp overdrive distortion presents an inherent problem: producing the desired distortion is inseparably connected to playing loudness and the wattage of any given amplifier. As a result, a player very often found that he had either too little, or too much wattage at his disposal to “get his tone” in different venues at the appropriate loudness level.
While earlier solutions to this problem of separating overdrive distortion from playing loudness have been introduced, the Gold Standard of tone and legitimacy remains—not preamp, but overdriven vacuum tube power amp distortion.
In an effort to remedy the problem of overdrive distortion being dependent on loudness, the present inventor has previously introduced methods to halve the wattage of a power amplifier. One such method is to include in a push-pull amplifier, switching between pentode and triode configurations, triode operation having approximately half the wattage of pentode. A further method utilizing a four-tube push-pull parallel amplifier is to selectively disable one pair of output tubes. Although these methods are helpful, their shortcoming is that they can only halve the power and in a great many applications, this limitation falls well short of fulfilling the need for a greater degree of power reduction to suit different venues and musical styles.